Phylloxera galls on hickory and pecan are usually large (up to 5/8 inch) and spherical, somewhat flattened or irregular in shape. The galls are hollow and are green outside and white inside. As the galls dry out, they darken and split open.
Various species of hickory and pecan (pecan is actually a species of hickory) are susceptible to phylloxera galls. Damage caused by phylloxera is primarily aesthetic. Galls on the leaf stem distort the leaf, sometimes grotesquely. As these galls mature and dry out, infested leaves die and drop prematurely. The canopy of heavily infested trees becomes filled with distorted, dying leaves, and the area around the tree becomes littered with fallen leaves.
The winter is spent in the egg stage inside the dead female on the bark in cracks and crevices and in the crevices of old galls or as eggs on fallen leaves and elsewhere. Nymphs hatch from these eggs in spring as the buds swell. The tiny new phylloxera nymphs crawl into the expanding buds and feed on the tender tissue. Feeding causes the plant tissue to form galls around the insects.
When mature, the phylloxera then lay eggs inside the galls from which hatch more phylloxera. The gall ultimately becomes filled with these insects as they grow. Finally, the galls split open and the phylloxera emerge to lay eggs on the leaves. From these eggs hatch male and female phylloxera which mature and then mate. These females lay eggs and die or die each with a single egg inside the abdomen.
No pesticide is currently labeled for phylloxera gall control on hickory. Several insecticides are labeled for pecan phylloxera on pecan: carbaryl (Sevin), lime-sulfur, malathion, horticultural oil and a few others. Commercial growers may use Provado, Warrior, or Lorsban. Consult the NC Agr. Chemicals Manual (see below) for other choices. The proper time to apply these pesticides is just as the buds are breaking and growth is resuming in the spring. It is rarely worthwhile to try to treat hickories for phyloxera galls.
If hickories infested with phylloxera are examined closely, it is often possible to detect scale insects for which horticultural oils are labeled. If horticultural oils are applied in the dormant season, scales (and phylloxera eggs) can be controlled. Such applications should be made during the fall, winter or early spring when no buds are open and leaves are not on the tree. Cover the trunk, main branches and smaller branches as thoroughly as possible. Be sure to follow the directions for safe use found on the label of whatever pesticides are used.
LSU Information Note
Missouri Information Note
Published by North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
ENT/ort-49 December 2000
Web page last reviewed January, 2011 by Art Vandolay.